The present invention relates to an electronic musical instrument and, in particular, to a key depression recognition system of such an instrument.
Numerous electronic musical instruments are known which are provided with keyboards similar to those of conventional pianos. Such instruments comprise multiplex circuitry for periodically scanning pickup circuits allocated to each key. In its most simple form, such a pickup circuit comprises a pair of contacts closed (or opened) upon key depression. Contacts, of course, have poor reliability, particularly in an instrument which is in use over a period of years without being serviced. A system using optoelectronic pickup means to provide improved reliability is disclosed in German (Federal Republic) Pat. No. 30 07 156. Both systems, however, permit only the recognition of whether or not a key has been depressed.
It is desirable to obtain information about the depression dynamics, i.e. about the force or speed of key depression, in addition to recognition of the fact that a key has been depressed. U.S. Pat. No. 3,652,774 discloses an instrument having a first pickup means for identifying the depressed key comprising a coil in which, upon key depression, a voltage is induced by means of a permanent magnet mounted on the key. A second pickup means to provide depression dynamics information comprises a pressure-sensitive resistor, and the voltage drop over it is processed when the key exerts pressure. Such voltage drop varies with the pressure so that the player can produce special effects, even with the key being already depressed, by varying the depression holding force. A similar system is disclosed in U.S. Pat. No. 4,520,706 where the only pickup means is such a pressure-sensitive resistor. It will be understood that reliability problems are encountered with such deformable resistors also, and that their production tolerances lead to difficulties in the manufacturing process.